I decided to patch the huge cracks in my upstairs hallway plaster last weekend. I watched three different videos of professional plasterers making it look incredibly simple. They just wiped the compound over the cracks and it looked like glass.
I bought a bag of setting type joint compound that you have to mix with water yourself. The bag specifically says it has a forty five minute working time. That is a complete lie.
I mixed a huge batch in a plastic bucket using cold water from the bathroom sink. It looked like thick pancake batter. I carried it out to the hallway and started applying the fiberglass mesh tape over the worst cracks. By the time I picked up my trowel to actually put the mud on the wall, the bucket was already getting warm. Ten minutes later the compound was literally turning into a solid rock.
I tried to spread it anyway. It dragged across the wall and left deep gouges everywhere. I ended up scraping most of it back off while it was still wet and dropping it directly onto my canvas tarp.
I had to throw the entire bucket out into the backyard. You cannot wash setting compound down a sink or it will permanently destroy your plumbing. Now I just mix tiny batches in a small plastic mud pan. I can only do a three foot section of the wall at a time. It takes forever but at least I am not throwing heavy rocks of dried plaster into the garbage every hour. The hallway still looks terrible. I will probably have to sand the whole thing down and start over next weekend.